1. Field of the Invention
The invention relates to an improved fuel injection valve for an internal combustion engine, which reduces exhaust emissions such as HC by atomizing the fuel spray.
2. Description of the Related Art
In an internal combustion engine such as an automobile engine, finer spray results in fuel burning more completely, which in turn results in greater engine performance and less exhaust emissions.
Japanese Patent Application Publication No. JP-A-9-32695 (Japanese Patent No. 3156554) discloses a structure in which the flow of fuel through a cylindrical fuel seal portion (a needle) (i.e., vertical flow) is converted into a flow between a flowrate measuring portion and the needle (i.e., lateral flow) and the fuel is led to a nozzle hole as it flows toward the center of the fuel injection valve. A strong vortex flow is generated by splitting the flow at the needle-side entrance port of the nozzle hole. This strong vortex flow helps to atomize the spray.
Because this method splits the flow of fuel on the needle side of the nozzle hole, however, the flow tends to concentrate at the inside wall surface of the nozzle hole on the center side of the fuel injection valve, which may increase the thickness of a fuel liquid film flowing over the inside wall of the nozzle hole. If this fuel liquid film becomes thick, it takes a lot of energy to break up the liquid film injected from the nozzle hole into particles. Therefore, the fuel liquid film is not easily broken up into spray particles immediately after injection. That is, the fuel liquid film is injected as a thick liquid film (in a liquid cylinder shape) so it takes time to break up into spray particles, which inhibits atomization.
The reason why the fuel liquid film is injected in this state is because the surface tension relationship between the fuel and the inside wall surface (which is usually stainless steel or the like) of the nozzle hole makes it difficult for the fuel to spread along the inside wall surface, and as a result, the fuel liquid film is distributed toward the side where the flow is strong on the nozzle hole inside wall surface such that the thickness of the fuel film becomes uneven.
Japanese Patent Application Publication No. JP-A-11-343481 discloses technology in which an oil repellant coating is applied to the inside wall of a nozzle hole in order to suppress fuel deposits from forming thereon, and Japanese Patent Application Publication No. JP-A-2003-227445 discloses technology in which a groove that is perpendicular to the direction in which fuel flows is formed on the inside wall of the nozzle hole in order to realize atomization. Neither of these technologies, however, achieve sufficient atomization effects so further improvement is necessary.
Further, in contrast to Japanese Patent Application Publication No. JP-A-11-343481, Japanese Patent Application Publication No. JP-A-2004-346817 discloses technology for improving spray atomization by applying a titanium oxide coating that has a lipophilic property to the inside wall of the nozzle hole. The problem with this technology, however, is that it results in increased pressure loss.